The present invention relates to siloxane quaternary ammonium salts.
Traditional melt-extrusion processes for the formation of a nonwoven web from a thermoplastic polymer typically involve melting the thermoplastic polymer, extruding the molten polymer through multiple orifices to form a plurality of threadlines or filaments, attenuating the filaments by entrainment in a rapidly moving first stream of gas, cooling the filaments with a second stream of gas, and randomly depositing the attenuated filaments, or fibers, on a moving foraminous surface. The most common and well known of these processes are meltblowing, coforming, and spunbonding. The nonwoven webs obtained by these processes are widely used in a variety of products, but especially in such disposable absorbent products as diapers; incontinent products; feminine care products, such as tampons and sanitary napkins; wipes; sterilization wraps; surgical drapes and related materials; hospital gowns and shoe covers; and the like, to name but a few.
There is an increasing interest in the utilization of nonwoven webs which have antimicrobial properties. The traditional means for providing such webs has been to simply topically treat the already-formed nonwoven web with a solution of an antimicrobial agent. This involves additional processing steps and typically requires drying the treated web to remove water or other solvent in which the antimicrobial agent is dissolved. Because the antimicrobial agent typically is water soluble, it is easily removed from the web by water. This obviously is a serious disadvantage for nonwoven webs which will be repeatedly used or placed in contact with water.
It is, of course, known to melt-extrude a mixture of an additive and a thermoplastic polymer to prepare fibers. In some instances, the additive must be forced, or "bloomed", to the surfaces of the fibers by subjecting them to a post-heat treatment step. The additive to be bloomed usually is a nonionic surfactant, such as an alkylphenoxy polyether.
In other instances, a surface-segregatable, melt-extrudable thermoplastic composition is employed which includes at least one thermoplastic polymer and at least one additive which typically is a polysiloxane polyether. Such surface segregation now appears to be best explained on the basis of micelle formation. Briefly, a relatively low molecular weight additive is miscible with the polymer at melt extrusion temperatures, forming an unstable emulsion characterized by metastable micellar structures. Upon extrusion, during which a rapid increase in shear rate is experienced, the additive is believed to break free from the metastable micelle "aggregate" and molecularly diffuse to the fiber surfaces. Such diffusion is driven in part by both a loss of additive compatibility and a potential drop in interfacial free energy.
However, the goal of providing a compound to be included as an additive in a thermoplastic composition for the preparation of antimicrobial nonwoven webs presents at least three challenges. First, the additive should undergo surface segregation upon melt-extruding the additive-containing thermoplastic composition to form fibers. As already noted, the compounds of the present invention do, in fact, migrate to the fiber surfaces. The alternative is to use an amount of the additive which is sufficiently large so as to assure that at least some additive is present at the surfaces of the fibers, but this significantly increases fiber spinning problems and increases the possibility of additive degradation. In addition, both material and manufacturing costs are increased. Second, assuming the additive is present at the surfaces of the fibers, it must be capable of imparting antimicrobial properties thereto. Third, the additive must be relatively stable during the melt-extrusion process.